Ten years later, responders who breathed the toxic dust and noxious fumes at New York City’s Ground Zero while searching for survivors are still suffering the effects of the attacks. The environmental hazards at the World Trade Center disaster site – mercury from fluorescent light bulbs, dioxin and benzene emitted as the jets burned, asbestos from the building materials, and more – have caused post-traumatic symptoms, severe respiratory ailments, immune problems and, some suspect, a greatly increased cancer risk. Chief medical correspondent Dr. Sanjay Gupta’s investigation reveals the consequences of 9/11’s killer dust – and what the experience may mean for the next time disaster strikes.